There is a trend amongst commercially available granular detergents towards higher bulk densities and towards granular detergent compositions which have a higher content of detergent active ingredients, such as various surfactants. Such detergents offer greater convenience to the consumer. The desire for such concentrated products ensures that the amount of filler materials are reduced and packaging materials which, ultimately, be disposed of.
Amongst consumers there is also a need for detergents which provide improved cleaning and stain removal. Therefore, in the recent past detergents have been developed which contain high levels of surfactant and various types of surfactants, such as anionic, nonionic and cationic surfactants.
The high density detergents, comprising high levels of surfactants can lead to poor solubility properties, arising from low rate of dissolution or the formation of gels, and thus to poor dispensing of the product, either from the dispensing drawer of a washing machine, or from a dosing device placed with the laundry inside the machine. This poor dispensing is often caused by gelling of particles, which have high levels of surfactant, upon contact with water. The gel prevents a proportion of the detergent powder from being solubilized in the wash water which reduces the effectiveness of the powder. This is a particular problem at low water pressures and/or at lower washing temperatures.
WO94/28098 discloses a non-spray-dried detergent powder comprising a combination of an ethoxylated primary C8-18 alcohol, an alkali metal aluminosilicate builder and 5 to 40 wt % of a water-soluble salt of a citric acid. EP-A-0 639 637 discloses the replacement of perborate bleach with an alkali metal percarbonate to improve the dispensing profile and dissolution rate of a detergent. Citrate or mixtures of citrate with sulphate or carbonate can be used to coat the percarbonate bleach. EP-A-0 639 639 contains a similar disclosure in this respect.
The use of effervescence to improve the dispensability of granular materials has been used extensively in pharmaceutical preparations. The most widely used effervescent system in this respect is citric acid in combination with bicarbonate. This effervescent system has also been described for improving the dispersibility of pesticidal compositions for controlling water-borne pests, e.g. GB-A-2,184,946.
EP-A-0 534 525 discloses the use of particulate citric acid with a specified particle size range of 350 to 1500 microns.
U.S. Pat. No. 5,114,647 discloses a sanitising composition comprising granules of alkali metal carbonate and aliphatic carboxylic acid of a particle size of 150 to 2,000 microns.
EP-A-0 333 223 discloses a bathing preparation comprising fumaric acid having an average particle size of 50-500 microns.
The addition of citric acid results in a reduction in alkalinity. However, an alkaline pH is required for an optimum performance of various detergent ingredients, such as certain surfactants. Overall an alkaline pH promotes cleaning, stain removal and soil suspension. Therefore, the incorporation of acids into detergent compositions is undesirable. For example, U.S. Pat. No. 4,414,130 discloses detergents, comprising organic acids, wherein certain compounds such as cationic surfactants are preferably omitted.
The Applicants now have found that the particular problems associated with dispensing a detergent composition comprising anionic and cationic surfactants can be improved by the inclusion of an acid and an alkali source whilst the performance of the cationic and anionic surfactants is maintained. This eliminates or reduces the problems of solid detergent particles remaining in the washing machine and on washed clothes.
Furthermore, since the surfactants are more efficiently dispensed into the wash water, the overall performance of the surfactants is more efficient and an overall improved cleaning, stain removal and soil suspending can be achieved.
Furthermore, the detergent residues in the dispensing drawer or dispensing device are reduced.
All documents cited in the present description are, in relevant part, incorporated herein by reference.